The present invention relates to an automotive exterior panel having a good appearance and smooth finish and to a method for producing the panel.
Conventional methods for producing hollow molded articles having a smooth appearance disclose a method comprising disposing a parison, which is composed of a noncrystalline resin exhibiting a tensile modulus of 2000 Kg/cm2 or more at 75xc2x0 C., between mold halves having mirror-finished cavity surface, closing the mold and closely adhering the parison to the cavity by blowing a pressurizing air into the parison, wherein the parison is adhered to the cavity which is set to a cavity temperature Yxc2x0 C. falling in the following range:
Yxc2x0 C.=(0.96 X0xe2x88x9237) to (0.96 X0+3)
where X0 is a temperature at which the tensile modulus of the noncrystalline resin is 2000 Kg/cm2 (Japanese Patent Application Publication (JP-B) No. 6-22875).
With this method it is impossible to avoid the formation of spot marks or line marks on the external surface of the hollow article of noncrystalline resin. Therefore, when producing an automotive exterior panel whose appearance needs to meet strict requirements, the spot marks and the line marks need to be removed by polishing or wet-sanding the external surface of the blow-molded hollow article of noncrystalline resin prior to the painting of the external surface. Consequently, the number of process steps increases and production costs become higher.
Another prior art method for thermoforming or blow molding a thermoplastic resin, is described in (JP-B No. 1-27849), wherein the gloss of the surface of the molded article is increased by heating selectively and instantly the mold surface to a temperature higher than the thermal deformation temperature of the resin by means of high frequency induction heating.
This method suffers has significant drawback, because it is necessary to use a special molding apparatus equipped with a mold heating device designed for the high frequency induction-heating. Consequently, the production costs become higher.
In (JP-B No. 2-40498), a method comprising blow-molding a molten parison, which has on the surface thereof many minute concavities/convexities having a depth in the range of from 2 to 100 xcexcm, by means of a mold which is heated to a temperature higher than the crystallization temperature of the resin and the surface of which is mirror-finished to a roughness of 0.5 xcexcm or less.
The melt fracture is generated on the parison surface so as to create many minute concavities/convexities having a depth in the range of from 2 to 100 xcexcm. The depth of the minute concavities/convexities are difficult to control, and the resulting article has a certain amount of surface roughness even after painting. However, the control of the melt fracture is difficult and therefore is not suited for mass production.
What is needed is an article that can be produced efficiently and in mass production that has a smooth appearance once painted, suitable for an automobile exterior panel. The process used to create such a panel should eliminate line marks, spot marks, and air marks. The process should allow for mass production and produce a cost-effective product.
The present invention has been achieved in view of the above-described problems of conventional technologies. It therefore is an object of the present invention to provide an automotive exterior panel which has excellent mechanical strengths, such as rigidity, and which presents a good appearance, free of coating imperfections such as orange peel, and allow painting without prior polishing or wet-sanding of the external surface of the blow molded hollow article.
Another object of the present invention is to provide a method for producing an automotive exterior panel.
In order to achieve the object, the first automotive exterior panel according to the present invention is an automotive exterior panel which is a blow molded article of a noncrystalline resin exhibiting a tensile modulus of 2000 Kg/cm2 or more at 75xc2x0 C. and which is coated with a 15 to 150 xcexcm thick paint film, wherein the panel to be coated has surface irregularities comprising a surface roughness in the range of from 0.9 to 9.0 xcexcm and an average peak-to-peak distance in the range of from 10 to 150 xcexcm.
In order to achieve the object, the second automotive exterior panel according to the present invention is an automotive exterior panel which is a blow molded article of a crystalline resin exhibiting a flexural modulus of 9000 Kg/cm2 or more at 23xc2x0 C. and which is coated with a 15 to 150 xcexcm thick paint film, wherein the panel to be coated has surface irregularities comprising a surface roughness in the range of from 0.9 to 9.0 xcexcm and an average peak-to-peak distance in the range of from 10 to 150 xcexcm.
Further, in the second automotive exterior panel, the crystalline resin exhibiting a flexural modulus of 9000 Kg/cm2 or more at 23xc2x0 C. may be incorporated with 3% to 35% by weight of an inorganic filler.
Still further, in the second automotive exterior panel, the crystalline resin exhibiting a flexural modulus of 9000 Kg/cm2 or more at 23xc2x0 C. is preferably polypropylene.
The first method of the present invention for producing the automotive exterior panel comprises the steps of producing a hollow molded article for automotive exterior panel by blow molding and painting the external face of the hollow molded article for automotive exterior panel, wherein a parison, which is composed of a noncrystalline resin exhibiting a tensile modulus of 2000 Kg/cm2 or more at 75xc2x0 C., is disposed between mold halves having minute concavities/convexities such that the surface roughness is in the range of from 0.9 to 9.0 xcexcm and the average peak-to-peak distance is in the range of from 10 to 150 xcexcm; the mold is then closed; and thereafter the parison is closely adhered by introducing thereinto a pressurized air to the cavity whose surface temperature is set to Yxc2x0 C. which falls in the following range:
Y=(0.96X+3) to (0.96X+40)
where X is a temperature at which the tensile modulus of the noncrystalline resin is 2000 Kg/cm2.
In the first method of the present invention for producing the automotive exterior panel, it is effective to set the cavity surface temperature Zxc2x0 C., at which a mold opening process is completed for taking out the molded article for automotive exterior panel, to a temperature in the range of Zxe2x89xa60.9X where X is a temperature at which the tensile modulus of the noncrystalline resin is 2000 Kg/cm2.
For clarity and understandability, the variables used for the noncrystalline resin are capital xe2x80x98Yxe2x80x99 and capital xe2x80x98Zxe2x80x99, while the variables used for the crystalline resin are lower case xe2x80x98yxe2x80x99 and lower case xe2x80x98zxe2x80x99.
The second method of the present invention for producing the automotive exterior panel comprises the steps of producing a blow molded article for automotive exterior panel by blow molding and coating the external face of the molded article for automotive exterior panel with a 15 to 150 xcexcm thick paint film, wherein a parison, which is composed of a crystalline resin exhibiting a flexural modulus of 9000 Kg/cm2 or more at 23xc2x0 C., is disposed between mold halves having minute concavities/convexities such that the surface roughness is in the range of from 0.9 to 9.0 xcexcm and the average peak-to-peak distance is in the range of from 10 to 150 xcexcm; the mold is then closed; and thereafter the parison is closely adhered by introducing therein a pressurized air to the cavity whose surface temperature is raised during the adhesion to y xc2x0 C. which falls in the following range:
A less than y less than 1.07B
where A is a peak crystallization temperature (xc2x0 C.) in a Differential Scanning Calorimetry (DSC) curve of the crystalline resin which exhibits a flexural modulus of 9000 Kg/cm2 or more at 23xc2x0 C.; and B is a peak fusion temperature (xc2x0 C.) in a DSC curve of the crystalline resin which exhibits a flexural modulus of 9000 Kg/cm2 or more at 23xc2x0 C.
The third method of the present invention for producing the automotive exterior panel comprises the steps of producing a blow molded article for automotive exterior panel by blow molding and coating the external face of the molded article for automotive exterior panel with a 15 to 150 xcexcm thick paint film, wherein a parison, which is composed of a crystalline resin exhibiting a flexural modulus of 9000 Kg/cm2 or more at 23xc2x0 C., is disposed between mold halves having minute concavities/convexities such that the surface roughness is in the range of from 0.9 to 9.0 xcexcm and the average peak-to-peak distance is in the range of from 10 to 150 xcexcm; a mold closing process is then started while raising the cavity surface temperature so as to reach a temperature y xc2x0 C. falling in the following range at a stage immediately before the closure of the mold:
A less than y less than 1.07B
where A is a peak crystallization temperature (xc2x0 C.) in a DSC curve of the crystalline resin which exhibits a flexural modulus of 9000 Kg/cm2 or more at 23xc2x0 C. while B is a peak fusion temperature (xc2x0 C.) in a DSC curve of the crystalline resin which exhibits a flexural modulus of 9000 Kg/cm2 or more at 23xc2x0 C.; the mold is then completely closed; and thereafter the parison is closely adhered to the cavity by introducing a pressurized air into the parison.
In the second method and in the third method of the present invention for producing the automotive exterior panel, it is effective to incorporate 3% to 35% by weight of an inorganic filler into the crystalline resin that exhibits a flexural modulus of 9000 Kg/cm2 or more at 23xc2x0 C.
Further, in the second method and in the third method of the present invention for producing the automotive exterior panel, it is effective to choose a temperature in the range of zxe2x89xa6Axe2x88x9215 for the cavity surface temperature (zxc2x0 C.) at which a mold opening process is started for taking out the molded article for automotive exterior panel.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only a preferred embodiment of the invention is described, simply by way of illustration of the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention.